NewRecorder makes and returns a new Recorder, which captures the DNS rcode from the ResponseWriter and also the length of the response message written through it.

NewServer starts and returns a new Server.

Recorder is a type of ResponseWriter that captures the rcode code written to it and also the size of the message written in the response.

A Server is an DNS server listening on a system-chosen port on the local loopback interface, for use in end-to-end DNS tests.